Avalanche Forecast

Archived

Mar 16th, 2016–Mar 17th, 2016

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

Olympics.

Dangerous avalanche conditions should persist above treeline, where recent wind slabs gradually stabilize. Conservative decision making will be essential Wednesday in higher open and exposed terrain as recent wind slabs gradually settle and stabilize. Avoid steep open slopes showing signs of recent wind transport. Best to confine travel to lower angled terrain away from wind effects.

Detailed Forecast

A few scattered showers are possible, but little accumulation is expected Wednesday. Temperatures should remain relatively cool, but expect increasing sun breaks to allow for daytime warming to have its effect on the snowpack.

Light to moderate westerly winds at ridge level should persist Wednesday, possibly redistributing available loose surface snow.

Recent wind slabs will be the main avalanche problems in the Hurricane Ridge area and vicinity.

New wind slab is mostly likely to be found on NW-SE facing slopes. Firm wind transported snow and snowpack cracking can be good signs of wind slab instabilities.

Increasing sun breaks may development wet surface snow as the sun is gaining power so watch for the development of loose wet snow on solar slopes during extended sun breaks.

The avalanche danger should continue to gradually decrease Wednesday with less wind and slow settlement and stabilization of new snow and fairly cool temperatures.

Snowpack Discussion

Weather and Snowpack

Storms have moved across the Northwest at a nearly daily frequency the past few weeks with fluctuating but generally moderate snow levels.

Two deep surface low-pressure systems moved across the Olympic Peninsula with the first passing last Thursday and the next on Sunday. These systems caused very stormy weather.

Cool showery weather Monday and Tuesday continued to deposit additional snow in showers at lower temperatures.

In the Hurricane Ridge area, about 2-3 feet or more of new snow has fallen since Thursday.

Periods of strong to very strong winds during recent storms created widespread wind and storm slab problems, creating dangerous avalanche conditions. These recent storms have also built large cornices along ridges.

Daytime warming and settlement have allowed storm snow weak layers to settle and stabilize, therefore, storm slabs have been removed from the avalanche problem list.

The mid and lower snowpack in the Olympics should generally be a stable mix of crusts and layers of moist and rounded snow crystals.

Recent Observations

NWAC pro-observer Matt Schonwald toured around the Hurricane Ridge area Friday. He found up to 20 cm of dense 1 F or P snow above the latest rain crust. Thin wind slab was generally not reactive except in isolated areas on N-NW lee aspects near treeline. Although cornices were large, they were generally firm and not sensitive. Matt observed evidence of a widespread natural cycle involving shallow slabs on northerly lee aspects that likely occurred Wednesday night during warming and a transition to rain. Windward slopes that had melted out a few weeks earlier had packed on a firm, and in places, icy thin cover. Overall Matt noted few current avalanche problems in the Hurricane Ridge area Friday.

Conditions should have changed drastically since last Friday however, after 1-2 feet more of snowfall.

Hurricane Weather Station

Internet communications to the station have been disrupted at the NWAC office. We have identified the problem and anticipate the station to return online sometime soon. We spoke too soon. We have an open trouble ticket with our internet provider and remain hopeful we will be back online shortly. We apologize for the outage and thank you for your patience.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.